Liquid flow monitoring system

ABSTRACT

The proposed technical solution relates to measuring technology and is intended for measuring levels of measured medium in various branches of industry. The technical problem solved by the claimed invention is the production of a capacitive level sensor which demonstrates high operational reliability and provides highly accurate measurements. The technical result achieved by using the claimed invention consists in overcoming the disadvantages of the prior art, increasing the reliability and manufacturability of the design and thus increasing the accuracy of interface level measurements.

FIELD OF THE INVENTION

The present disclosure proposed relates to measuring equipment, isdesigned to measure medium levels, and may be used in variousindustries.

BACKGROUND OF THE INVENTION

It is known as a capacitive liquid level sensor described in U.S. Pat.No. 3,901,079 published on Aug. 26, 1975, on 12 sheets (D1). Thecapacitive liquid level sensor known from D1 comprises a housing for thesensor's electronic computing equipment, connected to the housings forthe sensor's electrode probes.

The disadvantage of the sensor known from D1 is its low serviceabilityand high measurement error resulting mainly from the insufficientlyefficient and reliable design of the housing for the sensor's electrodeprobes.

BRIEF SUMMARY OF THE INVENTION

The technical problem to be solved by the claimed invention is to createa capacitive level sensor that features high serviceability and highmeasurement accuracy, can measure the level of liquid media withdifferent permittivity, and does not require further calibration.

The technical effect to be achieved by using the claimed invention is toeliminate the disadvantages of the prototype, to increase thereliability and manufacturability of the design and, consequently, toincrease the accuracy of level measurements, as well as to make itpossible to measure the level of liquid media with differentpermittivity without the need for further calibration of the capacitivesensor.

The technical effect is achieved by providing a capacitive level sensorcomprising: a base; a sensitive element; therewith the base comprises atleast: first part having a recess with a cover to hermetically house acomputing unit, as well as a hole for the computing unit's output cable;second part having holes for expansion sleeves mostly in the center, inthe area of the first part, holes for fasteners in the side, vent holesin the lateral side; therewith the sensitive element is an electrodehousing, which is a metal section formed by at least two tubes that areconnected to each other at least partially along the length of saidmetal section, which comprises at least one stiffener connecting atleast the two adjacent tubes of the section; therewith each tube of thesection has a slit aligned axially with the corresponding vent hole inthe lateral side and arranged at least partially lengthwise at least inone side adjacent to the measured medium; therewith the electrodehousing contains electrodes rigidly fixed in each tube of the section,and these electrodes are metal tubes having the same unit-lengthcapacitance but differing in their length, and the main electrode ismostly as long as the electrode housing, and each compensation electrodeis shorter than the main electrode; therewith the sensitive element isconnected to the base through holes for fasteners; therewith the mainelectrode and each compensation electrode are connected to the computingunit by means of metal rods connected to expansion sleeves, which areconnected to holes for expansion sleeves.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention are detailed below withreferences to the attached drawings, which are incorporated herein byreference.

FIG. 1 shows an exemplary general view of the preferred embodiment ofthe claimed capacitive level sensor.

FIG. 2 shows an exemplary general view of components constituting thepreferred embodiment of the claimed capacitive level sensor.

FIG. 3 shows an exemplary sectional view of the electrode housing forthe preferred embodiment of the claimed capacitive level sensor.

FIG. 4 shows an exemplary general view of the first alternativeembodiment of the claimed capacitive level sensor.

FIG. 5 shows an exemplary sectional view of the electrode housing forthe first alternative exemplary embodiment of the claimed capacitivelevel sensor.

FIG. 6 shows an exemplary general view of the second alternativeembodiment of the claimed capacitive level sensor.

FIG. 7 shows an exemplary sectional view of the electrode housing forthe second alternative exemplary embodiment of the claimed capacitivelevel sensor.

FIGS. 8 to 11 show an exemplary sectional view of the electrode housingfor other alternative exemplary embodiments of the claimed capacitivelevel sensor.

FIGS. 12 to 21 schematically show other exemplary sectional views of theelectrode housing for other alternative exemplary embodiments of theclaimed capacitive level sensor.

FIG. 22 shows an exemplary method for using a coupling sleeve for theelectrode housing of the capacitive sensor.

FIGS. 23 and 24 show an exemplary schematic diagram of the claimedcapacitive level sensor.

FIG. 25 shows an exemplary general diagram of a liquid flow monitoringsystem.

FIG. 26 shows the most typical exemplary placement of the claimedcapacitive level sensor in a reservoir with a measured medium.

FIG. 27 shows the most typical exemplary placement of the severalclaimed capacitive level sensors in a reservoir with a measured medium.

FIG. 28 shows the most typical placement of the several claimedcapacitive level sensors in an irregularly shaped reservoir with ameasured medium.

FIG. 29 shows the most typical exemplary placement of the claimedcapacitive level sensor in a vertical reservoir with a measured medium.

FIG. 30 shows an exemplary diagram for implementing the method forassembling the components of the claimed capacitive level sensor.

FIG. 31 shows an exemplary diagram for implementing the method forpre-calibrating the claimed capacitive level sensor.

FIG. 32 shows an exemplary diagram for implementing the method for levelmeasuring by means of the claimed capacitive level sensor.

DETAILED DESCRIPTION OF THE INVENTION

There are embodiments of the present invention below to explain itsimplementation examples in particular embodiments. Nevertheless, thisdisclosure itself is not intended to limit the scope of the rightsgranted by this patent. It should rather be assumed that the claimedinvention can also be implemented in other ways so that the claimedinvention will include different elements and conditions or combinationsof elements and conditions similar to the elements and conditionsdescribed herein in combination with other existing and futuretechnologies.

According to the preferred embodiment of the present invention, there isprovided a capacitive level sensor comprising a base; a sensitiveelement; therewith the base comprises at least first part having arecess with a cover to hermetically house a computing unit, as well as ahole for the computing unit's output cable; second part having holes forexpansion sleeves mostly in the center, in the area of the first part,holes for fasteners in the side, vent holes in the side; therewith thesensitive element is an electrode housing, which is a metal sectionformed by at least two tubes of equal or unequal length that areconnected to each other at least partially along the length of saidmetal section, which optionally comprises at least one stiffenerextending along the entire length of said metal section and connectingat least the two adjacent tubes of the section; therewith each tube ofthe section has either a vent hole aligned axially with thecorresponding vent hole in the lateral side of the collar part or a slitaligned axially with the corresponding vent hole in the lateral side ofsaid collar part and arranged at least partially lengthwise at least inone side adjacent to the measured medium; therewith the electrodehousing contains electrodes rigidly fixed in each tube of the section,and these electrodes are metal tubes having the same unit-lengthcapacitance but differing in their length, and the main electrode ismostly as long as the electrode housing, and each compensation electrodeis shorter than the main electrode; therewith the sensitive element isconnected to the base through holes for fasteners; therewith the mainelectrode and each compensation electrode are connected to the computingunit by means of metal rods connected to expansion sleeves, which areconnected to holes for expansion sleeves.

According to an alternative embodiment of the present invention, thereis provided said sensor, wherein the base is made of a metal orcopolymer or combinations thereof.

According to another alternative embodiment of the present invention,there is provided said sensor, wherein the connection between the metalrods and expansion sleeves is a thread joint.

According to another alternative embodiment of the present invention,there is provided said sensor, wherein the expansion sleeves are made ofa dielectric material.

According to another alternative embodiment of the present invention,there is provided said sensor, wherein the connection between theexpansion sleeves and holes for expansion sleeves is a thread joint.

According to another alternative embodiment of the present invention,there is provided said sensor, wherein the thread joint between theexpansion sleeves and holes for expansion sleeves contains a sealant.

According to another alternative embodiment of the present invention,there is provided said sensor, wherein the expansion sleeves havesealing rings.

According to another alternative embodiment of the present invention,there is provided said sensor, wherein the hole located in the recessand intended for the output cable of the computing unit contains asealant.

According to another alternative embodiment of the present invention,there is provided said sensor, wherein the vent holes are arrangedasymmetrically in terms of their vicinity to the base.

According to another alternative embodiment of the present invention,there is provided said sensor, wherein the main electrode and eachcompensation electrode are covered with an insulation wrap.

According to another alternative embodiment of the present invention,there is provided said sensor, wherein the sensitive element is formedby connecting at least two geometrically similar sensitive elements ofequal or unequal length by means of a coupling sleeve.

According to another alternative embodiment of the present invention,there is provided said sensor, wherein there are coaxial slits, whichare cut mostly along the entire length of the coupling sleeve body, ineach side of the coupling sleeve body adjacent to said slits in theelectrode housing.

According to another alternative embodiment of the present invention,there is provided said sensor, wherein the main electrode and eachcompensation electrode are made of the same material as the metal rods.

According to another alternative embodiment of the present invention,there is provided said sensor, wherein the main electrode and eachcompensation electrode, the metal rods, and electrode housing are madeof the same material.

According to another alternative embodiment of the present invention,there is provided said sensor, wherein each tube of the section has aslit along its entire length at least in one side adjacent to themeasured medium.

According to another preferred embodiment of the present invention,there is provided a sensitive element for the capacitive level sensor,being an electrode housing, which is a metal section formed by at leasttwo tubes of equal or unequal length that are connected to each other atleast partially along the length of said metal section, which optionallycomprises at least one stiffener extending along the entire length ofsaid metal section and connecting at least the two adjacent tubes of thesection; therewith each tube of the section has either a vent holealigned axially with the corresponding vent hole in the lateral side ofthe collar part of the base of the capacitive level sensor or a slitaligned axially with the corresponding vent hole in the lateral side ofsaid collar part of the base of the capacitive level sensor and arrangedat least partially lengthwise at least in one side adjacent to themeasured medium; therewith the electrode housing contains electrodesrigidly fixed in each tube of the section, and these electrodes aremetal tubes having the same unit-length capacitance but differing intheir length, and the main electrode is mostly as long as the electrodehousing, and each compensation electrode is shorter than the mainelectrode.

According to another alternative embodiment of the present invention,there is provided said sensitive element, wherein the main electrode andeach compensation electrode are covered with an insulation wrap.

According to another alternative embodiment of the present invention,there is provided said sensitive element that is formed by connecting atleast two geometrically similar electrodes of equal or unequal length bymeans of a coupling sleeve.

According to another alternative embodiment of the present invention,there is provided said sensitive element, wherein there are coaxialslits, which are cut mostly along the entire length of the couplingsleeve body, in each side of the coupling sleeve body adjacent to saidslits in the electrode housing.

According to another alternative embodiment of the present invention,there is provided said sensitive element, wherein the main electrode andeach compensation electrode, the electrode housing, and coupling sleeveare made of the same material.

According to another alternative embodiment of the present invention,there is provided said sensitive element, wherein each tube of thesection has a slit along its entire length at least in one side adjacentto the measured medium.

According to another alternative embodiment of the present invention,there is provided said sensitive element, wherein each tube of thesection has a slit along its entire length at least in one side adjacentto the measured medium.

According to another preferred embodiment of the present invention,there is provided an electrode housing for the capacitive level sensor,being a metal section formed by at least two tubes of equal length thatare connected to each other at least partially along the length of saidmetal section, which optionally comprises at least one stiffenerextending along the entire length of said metal section and connectingat least the two adjacent tubes of the section; therewith each tube ofthe section has either a vent hole aligned axially with thecorresponding vent hole in the lateral side of the collar part of thebase of the capacitive level sensor or a slit aligned axially with thecorresponding vent hole in the lateral side of said collar part of thebase of the capacitive level sensor and arranged at least partiallylengthwise at least in one side adjacent to the measured medium;

According to another alternative embodiment of the present invention,there is provided said housing, wherein each tube of the section has aslit along its entire length at least in one side adjacent to themeasured medium.

According to another preferred embodiment of the present invention,there is provided a measured medium flow monitoring system comprisingone or more capacitive level sensors installed in one or more reservoirswith measured media, wherein the sensors are configured to communicatewith a server to provide user information about the level in a reservoirin which said sensor is installed.

According to another alternative embodiment of the present invention,there is provided said system, wherein said capacitive sensors andserver communicate with each other by means of a transceiver.

According to another alternative embodiment of the present invention,there is provided said system, wherein the transceiver further comprisesone or more navigation unit connected to the server, and each navigationunit is associated with said single sensor or a single group of saidsensors and configured to transfer information about the location of thecorresponding sensor or group of sensors to the server.

According to another preferred embodiment of the present invention,there is provided a reservoir for a measured medium, containing saidcapacitive sensor optionally comprising said coupling sleeve.

According to another alternative embodiment of the present invention,there is provided a reservoir for a measured medium, containing one ormore said capacitive level sensors according to any of said embodimentsof the present invention.

According to another preferred embodiment of the present invention,there is provided a method for assembling the capacitive level sensor,consisting of the following steps: (A) connecting the capacitive sensorbase with expansion sleeves connected to metal rods; (B) installing thecomputing unit into the recess for the computing unit in the capacitivesensor base and connecting the computing unit with said metal rods; (C)connecting the output cable to the input of said computing unit; (D)installing the cover protecting the recess for said computing unit andsealing it with a compound through the threaded hole to connect theoutput cable; (E) screwing the output cable into said threaded hole; (F)pre-calibrating the capacitive sensor after the compound has cured; (G)screwing electrodes onto the metal rods; (H) installing the electrodehousing by stringing it on the electrodes and by rigidly fixing theelectrode housing in the collar part of the base, therewith theelectrodes may be optionally secured inside the electrode housing.

According to another preferred embodiment of the present invention,there is provided said method for assembling, wherein at step (F), thevalues obtained from the compensation measuring channels, which are oneor more channels formed by one or more of the metal rods, are normalizedby the value obtained from the main measuring channel, which is the onlychannel formed by only one of the metal rods, and correction factors arecalculated and recorded into the non-volatile memory of the computingunit.

According to another preferred embodiment of the present invention,there is provided said method for assembling, wherein the electrodehousing is rigidly fixed with pop rivets in the collar part of the base,and electrodes are secured with spacer rings inside the electrodehousing.

According to another alternative embodiment of the present invention,there is provided said method for assembling, wherein at step (G), theelectrodes are provided with insulation wrap.

According to another preferred embodiment of the present invention,there is provided a method for pre-calibrating the capacitive levelsensor during the assembly of the sensor, consisting of the followingsteps: (A) measuring the capacitance of the main measuring channel,which is only one of the metal rods connected to the computing unit ofthe capacitive sensor, as part of the pre-calibration procedure; (B)measuring the capacitance of each compensation measuring channel, whichis one or more of the metal rods connected to the computing unit of thecapacitive sensor, as part of the pre-calibration procedure; (C)calculating the differences between each capacitance value of thecompensation measuring channel and the capacitance value of the mainmeasuring channel by means of a microcontroller of said computing unit;(D) iteratively repeating the operations of steps (A) to (C) for aperiod in order to obtain a set of primary correction factors; (E)calculating the averaged value of the correction factor by means of saidmicrocontroller, based on the set of primary correction factors andstoring the resulting averaged value of the correction factor into thenon-volatile memory of said computing unit.

According to another alternative embodiment of the present invention,there is provided said method for pre-calibrating, wherein at step (D),the operations of steps (A) to (C) are repeated for a maximum of 30minutes.

According to another alternative embodiment of the present invention,there is provided said method for pre-calibrating, wherein at steps (A)and (B), the measured capacitance values may be optionally normalized bythe corresponding capacitance values at the reference temperature byusing the temperature compensation factor, the value of which haspreviously been recorded into the non-volatile memory of the computingunit, and at step (C), the resulting normalized capacitance values ofthe measuring channels are used as the capacitance values of themeasuring channels.

According to another preferred embodiment of the present invention,there is provided a method for level measuring by means of thecapacitive level sensor, consisting of the following steps: (A)calibrating the sensor in order to obtain calibration values of thecapacitance difference and values of the dynamic level range to berecorded into the non-volatile memory of the sensor's computing unit, byusing a measured reference medium; (B) measuring the level by means ofthe calibrated sensor, therewith the measurement consists of thefollowing steps: (B1) filling a reservoir with a measured medium to thelevel at which the longest compensation channel of the sensor is atleast partially immersed in the measured medium, while the measuredmedium differs from the reference medium; or filling a reservoir with ameasured reference medium to any permissible level for this reservoir;(B2) measuring the capacitance values of the main measuring channel andeach compensation measuring channel of the sensor for the reservoir thatcontains the measured medium, therewith each measurement of thecapacitance value of each compensation measuring channel is carried outtaking into account the average correction factor, the value of which isstored in the non-volatile memory of the computing unit; (B3)calculating values of the capacitance difference by means of themicrocontroller of the computing unit by using each capacitance value ofthe compensation measuring channel obtained at step (B2) and thecapacitance value of the main measuring channel obtained at step (B2)pairwise in order to obtain values of the capacitance difference; (B4)comparing the values of the capacitance difference obtained at step (B3)to the calibration values of the capacitance difference and calculatingthe ratio between these capacitance differences, which is the correctionfactor, by means of the microcontroller of the computing unit in orderto obtain the value of the correction factor; (B5) normalizing eachcapacitance value of the main measuring channel by the capacitance valueof the level by means of the microcontroller of the computing unit byusing the correction factor, the value of which was obtained at step(B4), in order to obtain the capacitance value of the level; (B6) usingthe resulting values of the level by means of the microcontroller of thecomputing unit in order to determine the relative level according to thevalues of the dynamic range.

According to another alternative embodiment of the present invention,there is provided said method for level measuring, wherein at step (A),the sensor is calibrated as follows: (A1) installing the sensor in areservoir that does not contain any measured medium; (A2) measuring thecapacitance values of the main measuring channel and each compensationmeasuring channel of the sensor for the reservoir that does not containany measured medium, therewith each measurement of the capacitance valueof each compensation measuring channel is carried out taking intoaccount the average correction factor, the value of which is stored inthe non-volatile memory of the computing unit; (A3) filling thereservoir with a measured reference medium to the maximum permissiblelevel for this reservoir; (A4) measuring the capacitance values of themain measuring channel and each compensation measuring channel of thesensor for the reservoir that contains the measured reference medium,therewith each measurement of the capacitance value of each compensationmeasuring channel is carried out taking into account the averagecorrection factor, the value of which is stored in the non-volatilememory of the computing unit; (A5) calculating calibration values of thecapacitance difference by means of the microcontroller of the computingunit by using each capacitance value of the compensation measuringchannel obtained at steps (A2) and (A4) and the capacitance value of themain measuring channel obtained at steps (A2) and (A4) pairwise, basedon the values obtained at steps (A2) and (A4), and recording theresulting calibration values of the capacitance difference into thenon-volatile memory of the computing unit; (A6) calculating a dynamiclevel range by means of the microcontroller of the computing unit, basedon the values obtained at steps (A2) and (A4) preceding to,simultaneously with, or after step (A5), with the dynamic level rangebeing the difference between the capacitance value of the main measuringchannel for the full reservoir and the capacitance value of the mainmeasuring channel for the empty reservoir, and recording the resultingvalues of the dynamic level range into the non-volatile memory of thecomputing unit.

According to another alternative embodiment of the present invention,there is provided said method, wherein to obtain normalized capacitancevalues of the measuring channels for the reservoir that does not containany measured medium at step (A2), the capacitance values of themeasuring channels measured at step (A2) are normalized by thecapacitance values of the measuring channels at the referencetemperature by means of the microcontroller of the computing unit byusing the temperature compensation factor, the value of which haspreviously been recorded into the non-volatile memory of the computingunit; to obtain normalized capacitance values of the measuring channelsfor the reservoir that contains the measured reference medium at step(A4), the capacitance values of the measuring channels measured at step(A4) are normalized by the capacitance values of the measuring channelsat the reference temperature by means of the microcontroller of thecomputing unit by using the temperature compensation factor, the valueof which has previously been recorded into the non-volatile memory ofthe computing unit; therewith at steps (A5) and (A6), the correspondingnormalized capacitance values of the measuring channels are used.

According to another alternative embodiment of the present invention,there is provided said method, wherein to obtain normalized capacitancevalues of the measuring channels for the reservoir that contains themeasured medium at step (B2), the capacitance values of the measuringchannels measured at step (B2) are normalized by the capacitance valuesof the measuring channels at the reference temperature by means of themicrocontroller of the computing unit by using the temperaturecompensation factor, the value of which has previously been recordedinto the non-volatile memory of the computing unit; therewith at step(B3), the corresponding normalized capacitance values of the measuringchannels are used.

According to another preferred embodiment of the present invention,there is provided a coupling sleeve for the electrode housing of thecapacitive level sensor, being a cylinder that follows the shape of thecross-section of the electrode housing of the capacitive level sensorpreferably in its cross-section or at least the cross-section of holesin its base and has slits in its side, which are cut mostly along theentire height of the coupling sleeve and span a larger area of thelateral surface.

According to another alternative embodiment of the present invention,there is provided said coupling sleeve, wherein slit-free portions ofthe coupling sleeve side are adapted not to obstruct the slits of theelectrode housing of said capacitive level sensor when connected to saidelectrode housing if the electrode housing of said capacitive levelsensor has slits.

According to another alternative embodiment of the present invention,there is provided said coupling sleeve that is made of the same materialas the electrodes, electrode housing, and connecting rods of thecapacitive level sensor.

As an example, but not a limitation, FIG. 1 shows an exemplary preferredembodiment of the claimed capacitive level sensor 100 (the sensor 100).As can be seen from FIG. 1, the claimed sensor 100 generally consists ofa base 1010 and an electrode housing 1020, which, when it containselectrodes, is the sensitive element of the sensor 100.

As an example, but not a limitation, FIG. 2 shows an exemplary generalview of components constituting one of the preferred embodiments of theclaimed sensor 100. As can be seen from FIG. 2, the componentsconstituting the sensor 100 may represent a base 1010; a housing 1020for electrodes 1031, 1032, optionally with at least one stiffener 1021and optionally with at least one coupling sleeve 1028 (FIG. 22);electrodes 1031, 1032 optionally with spacer rings 1033; expansionsleeves 1040 optionally with sealing rings 1041; connecting metal rods1050; a computing unit 1060.

The base 1010 is designed to house the computing unit 1060, which isdetailed below, and to connect the electrodes 1031, 1032 of the sensorto the input of the computing unit 1060. The base 1010 is most typicallyshaped as a collar flange, the first part of which, for example, withoutlimitation, is a flat part 1011 and may be of any shape (including acircle, ellipse, polygon, etc.), and the second part of which, forexample, without limitation, is a collar part 1012 and is shaped as,preferably, but not limited to, a hub with a bore of any shape(including a circle, ellipse, polygon, etc.). As it will become apparentto those skilled in the art upon reading the text below, the shape ofthe hub and, accordingly, that of the collar part 1012 bore are mainlydetermined by the cross-section shape of the housing 1020 for theelectrodes 1031, 1032 of the sensor and are selected to provide securefixation of the housing 1020 for the electrodes 1031, 1032 inside thecollar part 1012. Aside from this, the base 1010 does not have a throughhole in the center of the collar part 1012 as contrasted to aconventional collar flange, but has several threaded through holes (notshown in the drawings), the number of which corresponds to the number ofthe electrodes 1031, 1032 of the sensor. These threaded holes arearranged to provide such placement of the housing 1020 for theelectrodes 1031, 1032 that mounting holes 1022, 1023 of the tubes of thehousing 1020 for the electrodes 1031, 1032 are aligned axially with thecorresponding threaded holes. To fix the housing 1020 for the electrodes1031, 1032 to the collar part 1012, there are holes 10121 for fasteners,which may be, not limited to, pop rivets, in the collar part's sides.Aside from this, the collar part 1012 has preferably, although notnecessarily vent holes 10122 in its opposite sides as well. These ventholes are preferably arranged asymmetrically in terms of their vicinityto the flat part 1011 and are designed to allow a gas (a mixture ofgases) to enter the housing 1020 for the electrodes 1031, 1032 and toprovide the same level of a measured medium in communicating vessels,one of which is said housing 1020, and the other is a reservoir for ameasured medium. Aside from this, the flat part 1011 has a recess 1013for the computing unit 1060 on the side reverse to the side on which thecollar part 1012 is located. As it will become apparent to those skilledin the art upon reading the text below, the recess 1013 may be of anyshape (including a circle, ellipse, polygon, etc.), and it is mainlydetermined by the shape of the printed circuit board of the computingunit 1060. Nevertheless, the shape of the recess 1013 should allow therecess to be securely sealed with a compound after the installation ofthe computing unit 1060, followed by the installation of a cover 1014for the recess 1013. Aside from this, the shape of the recess 1013should allow a connector-equipped output cable 1063 of the computingunit 1060 to go through a hole 1015 in the recess 1013. Aside from this,the recess 1013 with the computing unit 1060 installed therein andcovered with the cover 1014 for the recess 1013 may be further coveredwith a cover 1070 preferably made of copolymer materials, such aspolyacetal, polyamide, polycarbonate, or similar materials, and shapedto provide for sufficient coverage of the recess 1013.

The base 1010 is preferably made of a metal. Nevertheless, if sufficientstiffness is provided, the base 1010 may also be made of a copolymer orits combinations, including those with a metal. Preferably, the base1010 is injection molded or milled.

The housing 1020 for the electrodes 1031, 1032 (the housing 1020) is ametal section formed by at least two tubes of equal or unequal (e.g.when there is no coupling sleeve, and the compensation electrode 1032 isshorter than the main electrode 1031) length that are connected to eachother at least partially along the length of said metal section. Thehousing 1020 may optionally comprise one or more stiffeners 1021 thatpreferably, although not necessarily extend along the entire length ofthe housing 1020 and are in contact with each tube or at least with twoadjacent tubes. Said tubes have mounting holes 1022, 1023, and inletholes 1024, 1025 (not shown in FIG. 2). As can be seen from FIG. 2,there are preferably vent holes 10201 in the place where said housing1020 connects to said collar part 1012 of said base 1010. These holesare to be aligned axially with the corresponding vent holes 10122 in thecollar part 1012, thereby allowing air to enter said housing 1020. Asidefrom this, each tube may have at least one slit 1026 (for example, FIG.3) arranged at least partially lengthwise at least in one side adjacentto the measured medium. The slit 1026 is preferably cut along the entirelength of each tube. The slit width is preferably up to 15 mm. Althoughit is also preferable that the slits 1026 in each tube are arrangedsymmetrically or at equal angles to each other, nevertheless, the slits1026 may be arranged otherwise, for example, without limitation, atunequal angles to each other. At the same time, the main purpose of theslits 1026 is to provide access of a measured medium to the housing 1020from the side of each tube containing the electrode 1031 or 1032. Onthis basis, the slits 1026 should be aligned axially with the vent holes10122 in the place where said housing 1020 connects to said collar part1012 of said base 1010, thereby allowing a gas (a mixture of gases) toenter said housing 1020. There are holes 1027 in the base of the housing1020. These holes are aligned axially with the holes 10121 in the collarpart 1012 of the base 1010, through which the housing 1020 and the base1010 are fastened together. Thus, as contrasted to the prototype andsimilar devices, the presence of the slit 1026 enables inertia-freemeasurements and rules out the clogging of the tube due to measuredmedium paraffinization, which will consequently lead to a greaterincrease in the reliability and manufacturability of the design as wellas to an increase in the accuracy of level measurements.

As an example, but not a limitation, FIG. 3-21 shows possible exemplarycross-sections of the tubes forming the housing 1020. In this case, itis preferable, although not necessarily that the shape of the electrodes1031, 1032 also changes depending on the tube cross-section tocorrespond to the cross-section of the tubes forming the housing1020—owing to this, a larger area of the capacitor can be provided,which will allow more accurate measurements. At the same time, althoughthe possible exemplary cross-sections of the tubes (see FIG. 3-21)forming the housing 1020 have the slits 1026, the tubes should have thecorresponding vent holes 10201, and the access of a measured medium tothe inside of said tubes is provided by the inlet holes 1024, 1025.Thus, said vent holes 10201 and slits 1026 are equivalent in theirprimary purpose. Given that the cross-section may be of any shape(including a circle, ellipse, polygon, etc. or their combinations) andthat there may be more than two electrodes 1031 or 1032, it should beapparent to those skilled in the art that the main principle ofdesigning the housing 1020 says that the housing 1020 should havesufficient bending stiffness as a whole, provide secure and rigidfixation of the electrodes 1031, 1032 inside the tubes and allow cuttingthe slit(s) 1026. These requirements are most relevant in the case of alarge length of the housing 1020, since a very long housing 1020 maybend along its length during operation, which will affect the geometryof the sensitive element formed by the outer surface of the housing 1020and electrodes 1031, 1032 placed inside its tubes. Such a change in thegeometry leads to a significant decrease in the measurement accuracy andreduces the serviceability of the sensor as a whole. To providesufficient bending stiffness, the housing 1020 may optionally besupplemented with at least one stiffener 1021. As previously stated,such a stiffener 1021 extends along the entire length of the housing1020 at the point of contact of at least two tubes. This stiffenerprovides further bending stiffness and prevents undesirable changes inthe geometry of the sensitive element. In some cases, for example, asshown in FIG. 5, 10, 11, 12, 21, the cross-section of the housing 1020is shaped to provide sufficient bending stiffness, and no stiffener 1021is required. The cross-section of the stiffener 1021 is also shaped toprovide sufficient bending stiffness of the housing 1020 as a whole. Asan example, FIG. 8, 14, 16, 17, 19, 20 show some cross-sections of thestiffener 1021 that differ from a circle.

The sensitive element of the sensor 100 is formed by placing theelectrodes 1031 and 1032 in the housing 1020, which thus form severalcapacitive measuring channels, one of which is the main channel, and therest are compensation channels. The electrodes 1031 and 1032 areidentical in their parameters, in particular, they have the sameunit-length capacitance, but they differ in their length. The electrode1031 is main and mostly as long as the housing 1020, while theelectrode(s) 1032 are compensatory and shorter, in particular, but notlimited to, much shorter than the electrode 1031. Preferably, theelectrodes 1031, 1032 are rigidly fixed inside the corresponding tubesof the housing 1020. In some cases, the electrodes 1031, 1032 may besecured by stringing spacer rings 1033 on them. These spacer ringsprotrude at their edges, so they at least partially form a stop to thetube wall and at least partially secure the ring with the protrusion inthe slit 1026. Said spacer rings 1033 are preferably placed in such away as to provide the best alignment of the electrode 1031 or 1032inside the corresponding tube of the housing 1020. At the same time, itshould be apparent to those skilled in the art that depending on thelength of the electrodes 1031, 1032, either one spacer ring 1033 (if theelectrode is short, as for the electrodes 1032) or several spacer rings1033 (if the electrode is long, as for the electrode 1031) may be usedto provide its rigid fixation inside the tube of the housing 1020. Atthe same time, it should be assumed that the number of spacer rings 1033should minimally affect the measurement accuracy, but fix the electrodes1031, 1032 inside the tubes of the housing 1020 rigidly enough tomaintain the stable geometry of the sensitive element of the sensor 100.

Said electrodes 1031, 1032 are tubes made of a metal. If the sensor 100is used for level measurements and one of the measured media is adielectric liquid, for example, not limited to kerosene, gasoline, otherfuels, then the electrodes 1031, 1032 do not require furtherimprovements. However, if the sensor 100 is used for level measurementsand one of the measured media is a conducting liquid, for example, notlimited to water, then the electrodes 1031, 1032 are further providedwith an insulation wrap along their entire length, such as, for example,not limited to a fluoroplastic sheath.

The measuring channels are connected to the input of the computing unit1060 by means of threaded metal rods 1050, on which expansion sleeves1040 preferably made of a dielectric material are screwed as shown inFIG. 2. The expansion sleeves 1040 may optionally have sealing rings1041. The upper part of the expansion sleeves 1040 is threaded, and thisallows a thread joint between said expansion sleeves and threaded holesin the flat part 1011 of the base 1010. Nevertheless, it should beassumed that the connection between the electrodes 1031, 1032, andcomputing unit 1060 must be sealed, and it should be apparent to thoseskilled in the art that only a particular implementation of such aconnection is demonstrated above. On the side of the recess 1013 (and,accordingly, on the side of the computing unit 1060), the metal rods1050, which are thus extensions of the electrodes 1031, 1032, areelectrically connected to the input of the computing unit 1060 byinstalling and fixing the electrodes 1031, 1032 in the expansion sleeves1040 by means of, for example, not limited to nuts, split washers or athread-locking fluid.

The length of the housing 1020 can be significantly increased with thecoupling sleeve 1028 (FIG. 22), which is a cylinder that follows theshape of the cross-section of the housing 1020 preferably in itscross-section or at least the general cross-section of holes in its baseand has coaxial slits 10281 in its side, which are cut mostly along theentire height of the coupling sleeve and span a larger area of thelateral surface. Thus, it should be assumed that such a coupling sleeve1028 minimally affects the general geometry of the sensitive element ofthe sensor 100, especially since said coupling sleeve is much shorterthan the housing 1020. At the same time, those portions of the couplingsleeve 1028 side that do not have the slits 10281 are designed in such away that when connected to the housing 1020, the slits 1026 of thehousing 1020 are not obstructed if they are in the housing 1020. Thecoupling sleeve 1028 is designed to securely and rigidly connect the twohousings 1020, which are identical in their geometry and optionally intheir length, to each other. For the electrode 1031 (and the electrode1032, if necessary), two parts of the electrode 1031 are connected toeach other by means of a metal rod 1029, for example, not limited to ametal rod similar to the metal rod 1050, with similar fasteners. Thecoupling 1028 is connected to the corresponding parts of the housing1020, for example, without limitation, by means of clamping screws10282.

Preferably, although not necessarily, the electrodes 1031, 1032, housing1020, coupling sleeve 1028, and connecting rods 1050 are made of thesame material.

The computing unit 1060 is used to generate a magnetic field in thesensitive element of the sensor 100 and to convert the received analogsignal into a digital signal, which can be transmitted to avisualization unit or a liquid flow monitoring system. As shown in FIGS.23 and 24, the computing unit 1060 most typically comprises an analogpart 1061 and a digital part 1062. The analog part 1061 most typicallycomprises an RC generator formed by resistors and capacitors of themeasuring channels 1031, 1032, an optional capacitive galvanic insulatorformed by capacitors C1, C3 and designed for protection against a shortcircuit at the input of the computing unit 1060 for cases where themeasured medium is flammable, an analog key 10611 designed to switchbetween the measuring channels 1031, 1032, therewith a larger number ofinputs of the analog key 10611 and, respectively, further capacitors toprovide further capacitive galvanic insulators may be provided dependingon the number of the measuring channels, a comparator 10612 designed todetect frequency pulses coming from the RC generator and having a higheramplitude than a certain preset threshold voltage and to calculate themsubsequently, a reference voltage source 10613 designed to provide astable reference voltage, an optional rectangular pulse generator 10614designed to equalize non-rectangular pulses detected by the comparator,and a galvanic insulator 10615 (of capacitive or inductive type)designed for protection against a short circuit at the output of theanalog part 1061 of the computing unit 1060 for cases where the measuredmedium is flammable. The digital part 1062 most typically comprises amicrocontroller 10621 connected to non-volatile memory 10622, a crystaloscillator 10623, and an interface 10624, for example, not limited to anRS-485 interface. At the same time, it should be apparent to thoseskilled in the art that the non-volatile memory, interface, and crystaloscillator may be either independent electronic components or componentsthat are part of the microcontroller as such. At the same time, as canbe seen from FIGS. 23 and 24, as an example, but not a limitation, thegalvanic insulator 10615 may be equipped with filtering power capacitorsdesigned to increase the reliability of the computing unit 1060 circuit.In turn, as an example, but not a limitation, the connection circuit ofthe non-volatile memory 10622 may comprise a resistor to provide theselection of the operating mode and a filtering power capacitor designedto increase the reliability of operation. In turn, as an example, butnot a limitation, the crystal oscillator 10623 may comprise a bindingtie formed by impedance-equalizing resistors designed to provide thefrequency stability of the crystal oscillator of capacitors. In turn, asan example, but not a limitation, the interface 10624 at the input ofthe computing unit 1060 circuit may comprise resistors for protectionagainst electrostatic and conductive interference, equipped withsuppressors (protective diodes) designed for protection againstelectrostatic discharges and conductive interference of large amplitude.

The digital signal generated by the computing unit 1060 duringmeasurements is transmitted via the output cable 1063 to a visualizationunit for displaying the current measurements and/or a liquid flowmonitoring system. As shown in FIG. 25, such a liquid flow monitoringsystem 200 may most typically comprise one or more sensors 100 and aserver 200. In this case, the sensors 100 are connected to a transceiver101 or a plurality of transceivers 101 providing a wired or wireless orcombined connection of the sensors 100 to the server 200. Such atransceiver is configured to transmit information coming from the outputcable 1063 of the sensor 100 to the server 200. In some cases, such atransceiver 101 may be equipped with navigation equipment to furthertransmit information about the location of the corresponding sensor 100to the server. In turn, the server 200, which is most typically acomputer device comprising a processor, memory, and optionallyinput/output devices, is configured to receive information from thecorresponding transceivers 101, process it, and provide informationabout the status and/or location of each sensor 100, including through aweb interface.

FIGS. 26 to 29 show exemplary ways of placing the sensor(s) 100 in areservoir 300 with a measured medium. Such a reservoir 300 may be anysuitable container, such as, but not limited to a canister, including afuel canister, a tank, including a fuel tank or a rocket fuel tank, atank vehicle, including a road tank vehicle or a rail tank car, areservoir, including a tanker tank or an underground tank, etc. Theupper wall of a suitable reservoir is at least partially solid. Thesensor 100 is rigidly mounted on the base 1010 in this solid part sothat the sensitive element (the housing 1020 with the electrodes 1031,1032) is vertically oriented and is located mostly in the central partof the reservoir 300. To provide sufficient measurement accuracy, thereservoir 300 may contain several sensors 100 (FIG. 27) depending on thereservoir 300 dimensions. Aside from this, the housing 1020 is extendedby means of a similar housing through the coupling sleeve 1028 (FIG. 29)depending on the reservoir 300 geometry. Aside from this, when usingseveral sensors 100 in one reservoir 300 of a mostly constant perimetergeometry (FIG. 27), it is preferable to place the sensors 100 inopposite corners of the reservoir. Aside from this, when using severalsensors 100 in one reservoir 300 of an inconstant perimeter geometry,e.g. with different heights in its different portions (FIG. 28), it ispreferable to place the sensors 100 in the center of each such portionas if only one sensor 100 is placed in one reservoir 300 of a mostlyconstant geometry.

As shown in FIG. 30, it is preferable to assemble the sensor 100 by amethod 400 for assembling as follows. At step 401, the expansion sleeves1040 connected to the metal rods 1050 are connected to the base 1010 bymeans of said threaded holes. Then, at step 402, the computing unit 1060is installed in the recess 1013. Then, at step 403, the output cable1063 is soldered to the computing unit 1060. After that, at step 404,the cover 1014 is installed to protect the recess 1013, this is followedby sealing with a compound through the threaded hole 1015. After that,at step 405, the output cable 1063 is screwed into the threaded hole1015. Once the compound has cured enough, at step 406, pre-calibrationis carried out, and the pre-calibration consists of normalizing thevalues obtained from the compensation measuring channels, which are oneor more channels formed by one or more of the metal rods 1050 at thisstep, by the value obtained from the main measuring channel, which isthe only channel formed by only one metal rod 1050 at this step,calculating correction factors and recording them into the non-volatilememory of the computing unit 1060. Then, at step 407, the electrodes1031 and 1032 are screwed onto the metal rods 1050, thereby providingtheir primary connection to the computing unit 1060. Now, at step 4071,the electrodes 1031, 1032 may optionally be insulated. After that, atstep 408, the housing 1020 is installed by stringing it on theelectrodes 1031, 1032 and rigidly fixed in the collar part 1012 of thebase 1010 by means of, for example, not limited to pop rivets, while theelectrodes 1031, 1032 are rigidly fixed inside the tubes of the housing1020 by means of spacer rings 1033.

As shown in FIG. 31, it is preferable to pre-calibrate the sensor 100 atstep 406 as follows.

At step 4061, the capacitance of the main measuring channel is measured.

At optional step 40611, to obtain the normalized capacitance value ofthe main measuring channel, the measured capacitance value of the mainmeasuring channel is normalized by the capacitance value at thereference temperature by means of the microcontroller of the computingunit 1060 by using the temperature compensation factor, the value ofwhich has previously been recorded into the non-volatile memory of thecomputing unit 1060.

At step 4062, the capacitance of each compensation measuring channel ismeasured.

At optional step 40621, to obtain the normalized capacitance value ofthe compensation measuring channel, the measured capacitance value ofeach compensation measuring channel is normalized by the capacitancevalue at the reference temperature by means of the microcontroller ofthe computing unit 1060 by using the temperature compensation factor,the value of which has previously been recorded into the non-volatilememory of the computing unit 1060.

At step 4063, to obtain values of primary correction factors, thedifferences between each (normalized) capacitance value of thecompensation measuring channel and the (normalized) capacitance value ofthe main measuring channel are calculated by means of themicrocontroller of the computing unit 1060.

At step 4064, to obtain a set of primary correction factors, theoperations of steps 4061 to 4063 are iteratively repeated for a certainperiod, which preferably does not exceed 30 minutes.

At step 4065, to obtain the value of the average correction factor, thisvalue is calculated based on the primary values of the correctionfactors from the set of primary values of the correction factors bymeans of the microcontroller of the computing unit 1060, and theresulting averaged value of the correction factor is recorded into thenon-volatile memory of the computing unit 1060 of the sensor 100.

As shown in FIG. 32, it is preferable to measure the level by a method500 for level measuring as follows.

At step 501, the sensor 100 is calibrated as follows.

At step 5011, the sensor 100 is installed in a reservoir that does notcontain any measured medium.

At step 5012, the capacitance values of the main measuring channel andeach compensation measuring channel of the sensor 100 are measured forthe reservoir that does not contain any measured medium, therewith eachmeasurement of the capacitance value of each compensation measuringchannel is carried out taking into account the average correctionfactor, the value of which is stored in the non-volatile memory of thecomputing unit 1060.

At optional step 50121, to obtain normalized capacitance values of themeasuring channels for the reservoir that does not contain any measuredmedium, the capacitance values of the measuring channels measured atstep 5012 are normalized by the capacitance values of the measuringchannels at the reference temperature by means of the microcontroller ofthe computing unit 1060 by using the temperature compensation factor,the value of which has previously been recorded into the non-volatilememory of the computing unit 1060.

At step 5013, the reservoir is filled with a measured reference mediumto the maximum permissible level for this reservoir.

At step 5014, the capacitance values of the main measuring channel andeach compensation measuring channel of the sensor 100 are measured forthe reservoir that contains the measured reference medium, therewitheach measurement of the capacitance value of each compensation measuringchannel is carried out taking into account the average correctionfactor, the value of which is stored in the non-volatile memory of thecomputing unit 1060.

At optional step 50141, to obtain normalized capacitance values of themeasuring channels for the reservoir that contains the measuredreference medium, the capacitance values of the measuring channelsmeasured at step 5014 are normalized by the capacitance values of themeasuring channels at the reference temperature by means of themicrocontroller of the computing unit 1060 by using the temperaturecompensation factor, the value of which has previously been recordedinto the non-volatile memory of the computing unit 1060.

At step 5015, based on the values obtained at steps 5012 and 5014 orbased on the normalized values obtained at steps 50121 and 50141,calibration values of the capacitance difference are calculated by meansof the microcontroller of the computing unit 1060 by using eachcapacitance value of the compensation measuring channel obtained atsteps 5012 and 5014 and the capacitance value of the main measuringchannel obtained at steps 5012 and 5014 pairwise or by using eachnormalized capacitance value of the compensation measuring channelobtained at steps 50121 and 50141 and the normalized capacitance valueof the main measuring channel obtained at steps 50121 and 50141pairwise, and the resulting calibration values of the capacitancedifference are recorded into the non-volatile memory of the computingunit 1060.

At step 5016, which may precede step 5015 or be carried out in parallelto step 5015, based on the values obtained at steps 5012 and 5014 orbased on the normalized values obtained at steps 50121 and 50141, adynamic level range is calculated by means of the microcontroller of thecomputing unit 1060, with the dynamic level range being the differencebetween the capacitance value of the main measuring channel for the fullreservoir and the capacitance value of the main measuring channel forthe empty reservoir, and the resulting values of the dynamic level rangeare recorded into the non-volatile memory of the computing unit 1060.

At step 502, the level is measured by means of the sensor 100 calibratedat step 501 as follows.

At step 5021, a reservoir is filled with a measured medium to the levelat which the longest compensation channel of the sensor 100 is at leastpartially immersed in the measured medium, while the measured mediumdiffers from the reference medium; or a reservoir is filled with ameasured reference medium to any permissible level for this reservoir.

At step 5022, the capacitance values of the main measuring channel andeach compensation measuring channel of the sensor 100 are measured forthe reservoir that contains the measured medium, therewith eachmeasurement of the capacitance value of each compensation measuringchannel is carried out taking into account the average correctionfactor, the value of which is stored in the non-volatile memory of thecomputing unit 1060.

At optional step 50221, to obtain normalized capacitance values of themeasuring channels for the reservoir that contains the measured medium,the capacitance values of the measuring channels measured at step 5022are normalized by the capacitance values of the measuring channels atthe reference temperature by means of the microcontroller of thecomputing unit 1060 by using the temperature compensation factor, thevalue of which has previously been recorded into the non-volatile memoryof the computing unit 1060.

At step 5023, to obtain values of the capacitance difference, the valuesof the capacitance difference are calculated by means of themicrocontroller of the computing unit 1060 by using each capacitancevalue of the compensation measuring channel obtained at step 5022 andthe capacitance value of the main measuring channel obtained at step5022 pairwise or by using each normalized capacitance value of thecompensation measuring channel obtained at step 50221 and the normalizedcapacitance value of the main measuring channel obtained at step 50221pairwise.

At step 5024, to obtain the value of the correction factor, the valuesof the capacitance difference obtained at step 5023 are compared to thecalibration values of the capacitance difference, and the ratio betweenthese capacitance differences, which is the correction factor, iscalculated by means of the microcontroller of the computing unit 1060.

At step 5025, to obtain the capacitance value of the level, eachcapacitance value of the main measuring channel is normalized by thecapacitance value of the level by means of the microcontroller of thecomputing unit 1060 by using the correction factor, the value of whichwas obtained at step 5024.

At step 5026, the resulting values of the level are used by means of themicrocontroller of the computing unit 1060 in order to determine therelative level according to the values of the dynamic range, which arestored in the memory of the computing unit 1060.

Obtaining the value of the average correction factor at step 4065 makesit possible to measure the level of media with a permittivity differentfrom the permittivity of the measured reference medium. Thus, owing tothe use of the average correction factor, the capacitive sensor does notrequire further calibration when the permittivity of the measured mediumchanges, for example, in case of changes in the fuel type orcharacteristics.

This disclosure of the embodiment of the claimed invention demonstratesonly alternative embodiments and does not limit other embodiments of theclaimed invention, since other possible alternative embodiments of theclaimed invention, which do not go beyond the scope of the informationset out in this application, should be apparent to those routinelyskilled in the art, for whom the claimed invention is designed.

1. A liquid flow monitoring system comprising one or more capacitivelevel sensors, wherein the sensors are configured to communicate with aserver to provide user information about the liquid flow through areservoir in which said sensor is installed, and wherein each saidcapacitive level sensor comprising: a base; a sensitive element;therewith the base comprises at least: first part having a recess with acover to hermetically house a computing unit, as well as a hole for thecomputing unit's output cable; second part having holes for expansionsleeves mostly in the center, in the area of the first part, holes forfasteners in the side, vent holes in the lateral side; therewith thesensitive element is an electrode housing, which is a metal sectionformed by at least two tubes that are connected to each other at leastpartially along the length of said metal section, which comprises atleast one stiffener connecting at least the two adjacent tubes of thesection; therewith each tube of the section has a slit aligned axiallywith the corresponding vent hole in the lateral side and arranged atleast partially lengthwise at least in one side adjacent to the measuredmedium; therewith the electrode housing contains electrodes rigidlyfixed in each tube of the section, and these electrodes are metal tubeshaving the same unit-length capacitance but differing in their length,and the main electrode is mostly as long as the electrode housing, andeach compensation electrode is shorter than the main electrode;therewith the sensitive element is connected to the base through holesfor fasteners; therewith the main electrode and each compensationelectrode are connected to the computing unit by means of metal rodsconnected to expansion sleeves, which are connected to holes forexpansion sleeves.
 2. The system of claim 1, wherein the base is made ofa metal or copolymer or combinations thereof.
 3. The system of claim 1,wherein the connection between the metal rods and expansion sleeves is athread joint.
 4. The system of claim 1, wherein the expansion sleevesare made of a dielectric material.
 5. The system of claim 4, wherein theconnection between the expansion sleeves and holes for expansion sleevesis a thread joint.
 6. The system of claim 5, wherein the thread jointbetween the expansion sleeves and holes for expansion sleeves contains asealant.
 7. The system of claim 4, wherein the expansion sleeves havesealing rings.
 8. The system of claim 1, wherein the hole located in therecess and intended for the output cable of the computing unit containsa sealant.
 9. The system of claim 1, wherein the vent holes are furtherarranged asymmetrically in terms of their vicinity to the base.
 10. Thesystem of claim 1, wherein the main electrode and each compensationelectrode are covered with an insulation wrap.
 11. The system of claim1, wherein the main electrode and each compensation electrode and theelectrode housing are made of the same material.
 12. The system of claim1, wherein each tube of the section has a slit along its entire lengthat least in one side adjacent to the measured medium.